Practicing Chiral Chromatography in Your Mobile Phase Comfort Zone

Transcription

1 Practicing Chiral Chromatography in Your Mobile Phase Comfort Zone

2 Enantiomers Stereoisomers that differ in the direction they rotate a plane of polarized light are called optically active, or chiral, and their isomers are called enantiomers They are non-superimposable mirror images They are Important because biological systems recognize chirality * Thalidomide * * Ephedrine * Carvone Two chiral molecules (enantiomers). The asymmetric carbon is the purple atom in the middle. 2

3 Distinguishing Between Enantiomers Enantiomers differ in two ways: 1. The direction they rotate a plane of polarized light 2. Their interaction with other chiral molecules: Biological molecules (e.g. proteins) Chiral HPLC & GC stationary phases 3. We can leverage these differences to separate enantiomers 3

4 Schematic of How Chiral Chromatography Works: 3-Point Interaction Enantiomers Cannot fit Cannot fit 4 Surface of a chiral stationary phase Retention Time

5 The Power of Chiral Chromatography These four compounds only differ in the orientation of the H and H groups, and demonstrate the ability of chiral HPLC to B separate enantiomers and diastereomers 2,3-Dihydroxy-3-phenyl-propionic Acid Isomers: B H H H H H H H H H H A A H H H H H H H H H H 5 racemate A -H groups on the same side racemate B -H groups on the opposite side column: CHIRBITIC R, 25 cm x 4.6 mm I.D., 5 µm particles (1324AST) mobile phase A:.1% ammonia, ph 4.1 with formic acid mobile phase B: methanol mobile phase ratio: 5:5 flow rate: 1 ml/min. temp.: ambient det.: UV at 258 nm injection: 1 µl

6 Chiral HPLC Chiral stationary phases for HPLC Familiar HPLC and LC-MS mobile phases Chiral screening and LC-MS Preparative considerations 6

7 Types of Chiral Stationary Phases (CSP) Chiral molecules Cellulose/amylose Macrocyclic glycopeptides Cyclodextrins Synthetic polymers Proteins Amino acids ther small, chiral molecules The more different types of functional groups in the CSP, the more types of interactions it can undergo with the analytes (more potential for success). 7

8 Cyclodextrin (CYCLBND) and Macrocyclic glycopeptide (CHIRBITIC) Innovative CSPs invented by Prof. Daniel Armstrong Naturally-occurring compounds Multiple chiral selectors tightly bonded to pure silica Versatile and extremely robust Use familiar mobile phases, like reversed-phase Useful for polar and ionic compounds MS-compatible; ionic mobile phases promote sensitive MS response Complement cellulose and amylose polysaccharide type columns Greener than normal phase 8

9 Success of Co-screening with Polysaccharide CSPs The cyclodextrin and macrocyclic glycopeptide CSPs are complementary to the more common polysaccharide CSPs. Generally: 25% chance that polysaccharide gives best separation 25% chance that the cyclodextrin and macrocyclic glycopeptide CSPs give best separation 5% overlap (both work) Macrocyclic glycopeptide & cyclodextrin CSPs (polar molecules dominate) Polysaccharide CSPs (nonpolar molecules dominate) 9

10 Cyclodextrin (Astec CYCLBND) -cyclodextrin or modified (derivatized) -cyclodextrin covalently bonded to porous silica 35 chiral centers Chiral, non-polar interior basket Chemical selectors on the outside surface Types of possible interactions: Hydrophobic inclusion Hydrogen bonding interactions Steric interactions Dipole-dipole interactions - interactions R R R R R R R R Silica Gel 1

11 Astec CYCLBND Derivatives R = Designation CD Type 11 none -CH 3 -CCH 3 H CH 2CHCH 3 * CH 3 CNH CH 3 2N CF 3 2 N CYCLBND I 2 CYCLBND II 2 CYCLBND I 2 DM (methylated) CYCLBND I 2 AC CYCLBND II 2 AC (acetylated) CYCLBND I 2 RSP or HP-RSP or SP (Racemic or S-hydroxypropyl ether) CYCLBND I 2 DMP (3,5-dimethylphenyl carbamate) CYCLBND I 2 DNP (2,6-dinitro-4-trifluoromethyl phenyl ether) Most successful selectors: CB I 2 HP-RSP DNP (Pi Acid) DMP (Pi Base)

12 Astec CYCLBND Separation Column: Astec CYCLBND I 2, 25 cm x 4. 6mm I.D., 5µm particles Mobile Phase: 25/75, ACN/2mM NH4Ac, ph 4. Flow Rate:.6 ml/min UV: 23 nm Temperature: 25 C Analyte: Mephenytoin H 3 C * H N N CH 3 Mephenytoin (an anticonvulsant) Time (min)

13 13 Astec CHIRBITIC Macrocyclic glycopeptides Multi-modal chiral surface capable of a wide variety of different interactions Unique ionic interactions very useful for polar and ionic compounds and mobile phases Very robust chemistry: Chemically bonded to pure silica (>4 linkages) Stable to high flows, solvents, temperature (5 C) and pressures (35 psi) Choices in enantioselectivity among 6 phases CH 2 H H H H HNCCH 3 H HN H HC H H CH 2 H Cl H H H N N H H CHIRBITIC T (Teicoplanin) H Cl Cl H H H H H H N N N N H H H H HN H HC H H H H NHR N H H H H H H Cl H N CH 2 H H H H N H H H N H H H CHIRBITIC TAG NH 2 NH 2

14 Astec CHIRBITIC Structures Space-filling molecular models Live area for full-page graphic (Delete this box when image is placed.) 14

15 Astec CHIRBITIC Phases Macrocyclic Glycopeptide Vancomycin Teicoplanin Ristocetin Teicoplanin Aglycone Designation Astec CHIRBITIC V and V2 Astec CHIRBITIC T and T2 Astec CHIRBITIC R Astec CHIRBITIC TAG 15

16 CHIRBITIC Separation Column: Astec CHIRBITIC V, 25 cm x 4. 6mm I.D., 5µm particles Mobile Phase: 1/9, ACN/2mM NH4Ac, ph 5.5 Flow Rate: 1 ml/min UV: 21 nm Temperature: 25 C Analyte: 5-Methyl-5-phenylhydantoin HN * NH Time (min) 16

17 Chiral HPLC Chiral stationary phases for HPLC Familiar HPLC and LC-MS mobile phases Chiral screening and LC-MS Preparative considerations 17

18 3-Point Interactions on Multi-modal CHIRBITIC and CYCLBND CSPs The most likely interactions between analyte and CSP in descending order of strength under different mobile phase conditions: Reversed Phase Conditions (all compounds) Ionic Hydrogen Bonding Steric/Inclusion/Hydrophobic Polar Ionic Conditions (ionizable compounds only) Ionic Hydrogen Bonding Steric/ - Polar rganic & Normal Phase Conditions (neutral compounds) Hydrogen Bonding - Steric/Dipole 18

19 Chiral Reversed-Phase Comprises water (buffers) with CH 3 H or CH 3 CN In most HPLC analysts comfort zone Highly compatible with mass spectrometry detection Especially valuable for the separation of polar and ionic chiral analytes Distinct and valuable benefits for preparative separations Greener more water, less hazardous solvents Many parameters to vary to optimize: ph Buffer type and concentration rganic modifier type and concentration Temperature Flow rate Permitted on CHIRBITIC and CYCLBND columns 19

20 Bupivacaine in Reversed-Phase Mode on CHIRBITIC V2 mau /2: MeH/1mM NH 4 Ac, ph 4.1 P1: 8.79 min. P2: 1.23 min. = 1.24 Large changes in % water may not change chiral retention and selectivity 1 5 5/5: MeH/1mM NH 4 Ac, ph 4.1 mau mau /75: MeH/1mM NH 4 Ac, ph P1: min.. 15 P2: min.. = min P1: 8.5 min. P1: 8.5 P2: P2: min. = min min 2 Although the polar ionic mode tends to give sharper peaks with less retention, CHIRBITIC phases can also provide the flexibility of using reversed-phase mode to control the retention (U-shape) and to increase sensitivity in LC-MS.

21 Conversion from Reversed Phase to Normal Phase Easily Accomplished RP * S CH 3 NP Methyl phenyl sulfoxide Using MtBE 21 Methyl phenyl sulfoxide separation by CHIRBITIC V (25x4.6mm). Top: 2/8, THF/2 mm NH4N3. Bottom: 97/2/1/, MtBE/ACN/MeH.

22 Unique Polar Ionic Mode for Astec CHIRBITIC Unique to CHIRBITIC CSPs Comprises methanol or acetonitrile with organic salt, acid or base e.g. 1 mm ammonium formate in methanol Ideal for LC-MS (volatile salts) Ideal for prep (volatile) Analytes are ionizable molecules any acid or base 22

23 Bupivacaine in Polar Ionic and Reversed-Phase Modes on CHIRBITIC V2 Mobile Phase: 1/.1w%: MeH/NH 4 Formate Mobile Phase: 1/.1w%: MeH/NH 4 TFA mau mau P1: 3.76 = 1.37 P2: 4.12 = P1: 5.33 P2: N NH CH 3 15 mau min Mobile Phase: 9/1: MeH/1mM NH 4 Ac ph 4.1 = min 2 P1: P2: H3 C 1 5 CH 3 min min 23 CHIRBITIC V2, 25x4.6mm

24 Buffer Component Ratio in Polar Ionic Mode Acid:Base = 1:1 Acid:Base = 3:1 Acid:Base = 1:3 24

25 Chiral HPLC Chiral stationary phases for HPLC Familiar HPLC and LC-MS mobile phases Chiral screening and LC-MS Preparative considerations 25

26 LC-MS Chiral Column Screening Strategy Chiral method development = Screening several columns! Impossible to predict which CSP will work LC-MS can make this easier by allowing mixtures of different enantiomers to be screened simultaneously CHIRBITIC and CYCLBND are compatible with LC- MS 26

27 Published Data 53 Chiral Compounds (Three CHIRBITIC and four CHIRALPAK columns) % Positive CSP Mobile Phases No. perating Parameters 87% CHIRALPAK AS, AD, D, J % CHIRBITIC V, T, R % Combined 7 26 Ref: Evaluation of Generic Liquid Chromatography Screens for Pharmaceutical Analysis, Andersson, M.E., Aslan, D., Clarke, A., Roeraade, J. Hagman, G., Journal of Chromatography A, 15 (23) CHIRACEL and CHIRALPAK are registered trademarks of Daicel Chemical Industries Ltd.

28 HPLC CHIRBITIC and CYCLBND Recommended Screening Columns Protocol includes three mobile phase conditions run with six different stationary phase chemistries as a front line screening*. This front line has generally provided ca. 8% screening success. Columns: Mobile Phases: CHIRBITIC TM V2 T TAG CYCLBND TM -CD DNP (or DMP) HP-RSP Polar Ionic Mode (PIM) 1:.1:.1, methanol:acetic acid:triethylamine Reversed-Phase (RP) 7:3, 2 mm ammonium acetate (ph 4.):acetonitrile Polar rganic Mode (PM) 95:5:.3:.2, acetonitrile:methanol: acetic acid:triethylamine. 28 * Protocol may be adjusted for LC-MS or for certain sample types.

29 Chiral LC-MS Column Screening Protocol LC-MS analysis Has ability to separate in the mass/charge dimension, making it possible to evaluate many analytes in the same injection. perates well in both reversed-phase and polar ionic/polar organic modes; ammonium salts usually preferred over TEA in mobile phases. Compatible with both the CHIRBITIC and CYCLBND CSPs. May be used as a valuable tool for rapid chiral screening of multiple chiral samples using simultaneous injection and selective ion detection. 29

30 Comparison of Metoprolol Alone and in 13-Component Chiral Mixture by LC-MS super sample_t_.1%aa in methanol _2 1: Scan ES e7 % _5 1: Scan ES e7 % Metoprolol Metoprolol with other compounds 6.51 Note a slight variation in enantiomer response due to ion-suppression by coeluting peaks; however, retention and selectivity is not compromised Time 3 CHIRBITIC T,.1% NH 4 Ac in Methanol (Polar Ionic Mode), ESI+ (Extracted Ion Current).

31 Changing Chiral Stationary Phase Provides Greatest Impact on Selectivity CHIRBITIC V2, TAG and R were screened to assess the impact of stationary phase on a set of basic analytes Instrument: Waters/Micromass ZQ, Single Quadrupole, Waters Alliance 269 Column: CHIRBITIC V2, TAG and R, 15 x 4.6 mm Temperature: 35 C Flow Rate: 1 ml/min Mobile Phase: Ammonium formate in methanol (13 mm) Detection: ESI, Positive Ion Mode, scan range m/z 15 5 Inj. Vol.: 5 µl 31

32 CHIRBITIC V2 Shows Selectivity for Fluoxetine and Norfluoxetine Unique selectivity between V2 phase and certain solutes shows up in LC-MS screen. chirobiotic V2 1535_68_6 1 % 3. 1: Scan ES e7 Verapamil 1535_68_6 1 % : Scan ES e7 Fluoxetine 1535_68_6 1 % 1535_68_6 1 % : Scan ES e : Scan ES e7 Norfluoxetine Pentazocine 1535_68_6 1 % : Scan ES e7 Time Chlorpheniramine 32

33 CHIRBITIC TAG Shows Selectivity for Amphetamines chirobiotic TAG 1535_68_14 1 % 1535_68_14 1 % 1535_68_14 1 % 1535_68_14 1 % 1535_68_14 1 % Unique selectivity between TAG phase and certain solutes shows up in LC-MS screen : Scan ES e : Scan ES e : Scan ES e : Scan ES e : Scan ES e6 Time Fenfluramine Normetanephrine MDA Chloramphetamine Synephrine 33

34 Impact of Buffer Component Ratio on Metoprolol Retention and Selectivity 13 mm ammonium hydroxide and 13 mm formic acid were independently prepared in methanol. 75:25 ammonia:formic 1535_ % base:acid ratio 1:3 1: Scan ES e7 1535_ % : Scan ES e :1 1535_ % : Scan ES e7 3:1 34 Time

35 Results of Fluoxetine Column Screen Spectrum Column mode elution (+/-)-Fluoxetine underwent the the primary screening protocol and and yielded yielded positive results. results CHIRBITIC TAG RP No Elution CHIRBITIC TAG PIM No Separation CHIRBITIC V2 RP Separation CHIRBITIC V2 PIM Separation CHIRBITIC T RP No separation F F F HN CH 3 CHIRBITIC V2 in both RP and PIM provided excellent selectivity while CYCLBND I 2 DNP showed some selectivity in RP CHIRBITIC T PIM No Separation Cyclobond I 2 RP No Retention Cyclobond I 2 PM No Separation Cyclobond 2 HP-RSP RP No Separation Cyclobond 2 HP-RSP PM No Separation Cyclobond 2 DNP RP Separation Screening results are viewed in a tabular form for easy review and comparison Cyclobond 2 DNP PM Unknown

36 Chiral HPLC Chiral stationary phases for HPLC Familiar HPLC and LC-MS mobile phases Chiral screening and LC-MS Preparative considerations 36

37 Prep Benefit: Low Flow Rate on CHIRBITIC ptimal linear velocity on CHIRBITIC is significantly lower than that observed on achiral (C18) columns. Low flows increase analysis time but greater efficiency and resolution increase sample capacity in prep separations. 37

38 Benefits of Low Flow for Fluoxetine on CHIRBITIC V2 vs. Ascentis C Reduced Plate Height Column Column Dimensions: Dimensions: x x mm, mm, 5 5 um um particle particle size size Reduced Linear Velocity C18 h (data fit theoretically to Knox) V2 h (data fit theoretically to Knox) C18 h (experimental) V2 h (experimental) 38 The optimal reduced linear velocity on the V2 is.61, which translates into a flow rate of.15 ml/min on the analytical column used in this study.

39 Low Flow Advantage: Three Examples Mobile Phase: 1%MeH 1/.1w%, MeH/NH4formate Sample: 5,5 hydantoin terbutaline clenbuterol Column: CHIRBITIC T, 5u, 25cmx4.6mm Flow Rate (ml/min) Plate Counts (peak 1) % Gain, Y/G 58% 96% 79% 39

40 Prep Benefit: Reversed-Phase Mode Improved solubility of polar analytes Preparative work cannot be completed if the sample cannot be dissolved in the solvent Less toxic than normal phase Reversed-phase: mobile phase is mostly aqueous Normal phase: 1% organic solvents and usually between 7% and 1% hexane or heptane Hexane has been known to produce neurotoxic effects 4

41 ptimizing Separation of Fluoxetine for Preparative HPLC Conditions: Column: CHIRBITIC V2, 15 x 4.6 mm, 5 µm particles Mobile Phase: 7:3, 2 mm NH 4 Ac (ph 4): ACN (Reversed-Phase Mode): Sample: 12.5 mg/ml in mobile phase (racemic) Injection Volume: 2 L To optimize efficiency Flow Rate:.15 ml/min. F F UV 23 nm F Temperature: 1 ºC To increase Rs HN CH 3 Peak 1 retention time (R t1 ): Peak 2 retention time (R t2 ): = min min Time (min)

42 Fluoxetine Prep Separation with Stacked Injections Conditions: Column: CHIRBITIC V2, 25 x 21.2 mm, 5 µm particles Mobile Phase: 7:3, 2 mm NH 4 Ac (ph 4): ACN (Reversed-Phase Mode): Sample: 5 mg/ml in mobile phase (racemic) Injection Volume: 88 L Flow Rate: 3.2 ml/min UV 23 nm Temperature: 1 ºC SPD -1Avp C h1-23nm SPD -1Avp C h1-23nm SPD -1Avp C h1-23nm SPD -1Avp C h1-23nm (+/-)-flu o xetin e (+/-)-flu o xetin e (+/-)-flu o xetin e (+/-)-flu o xetin e Retention T im e (mv) 1 45 psi Minutes

43 Sample Recovery in RP and PIM Modes Reversed-Phase: Problems: Lengthy time to remove water by evaporation Buffer sales Solution: Trap eluant containing analyte on C18 flash cartridge, wash Elute in a minimal amount of MeH Polar Ionic Mode: Problems: Mobile phase additives (salts) Solutions: Concentrate, dissolve in diethyl ether Load onto a silica flash cartridge, wash Elute with a minimal amount of MeH 43

44 Sample Recovery Using Reversed-Phase C18 Flash Column Method 16 ml fractions collected Evaporation Analyte adheres to C18 Elution with methanol 1-2 hrs 3 ml of of analyte in in methanol Evaporation 44 NP > 1.5 hrs PIM/PM > 3 hrs RP > 8 hrs ~ to to 2 2 minutes

45 Purity of Prep Fractions Peak 1: Enantiomeric Purity: 99.9% Time (min) Peak 2: Enantiomeric Purity: 99.4% Time (min)

46 Important Points in Reversed-Phase Chiral Preparative Separations Use of reversed-phase and polar ionic/polar organic modes for prep separation at low flow rates are safe and efficient ways to execute successful chiral preparatory separations. Fast sample recovery from prep in RP using C18 recovery method RP less toxic than NP Low flow improves efficiency 46

47 verall Chiral Summary Chiral stationary phases for HPLC CYCLBND CSPs: Covalently bonded -cyclodextrin or derivatized -cyclodextrin Reversed-phase, polar organic mode, normal phase modes CHIRBITIC CSPs: Macrocyclic glycopeptides Especially useful for separation of polar analytes Reversed-phase, polar-ionic, or normal phase modes Robust and compatible with all HPLC solvents MS detection and prep compatible Familiar HPLC and LC-MS mobile phases Solvents and conditions familiar to most analytical chemists MS compatible Ideal for separation of polar and ionic compounds 47

48 CHIRBITIC HPLC Columns LC-MS compatible RP mobile phases Analytical to prep Phases: CHIRBITIC T and T2 CHIRBITIC V and V2 CHIRBITIC TAG CHIRBITIC R Complements other Astec phases, CYCLBND, P-CAP, and chiral GC Analytical Services 48

49 Supelco Chiral Services Chiral column screening (HPLC & GC) Method optimization Small-scale purification (<1 grams of each enantiomer) Larger scale through our SAFC partners 49

50 Acknowledgements/Collaborators Prof. Daniel Armstrong, U. Texas Arlington Dick Henry, Consultant Supelco and Fluka R&D Teams For more information on the subjects presented here, please contact or your regional sales team. 5